| Electronically controllable rf switch -> Monitor Keywords |
|
|
  Electronically controllable rf switchUSPTO Application #: 20060208826Title: Electronically controllable rf switch Abstract: An RF switch circuit (10) and a turner (12) comprising an RF switch circuit are described. The switch circuit comprises at least two input terminals and one output terminal. The input terminals are connected to different RF signal sources, e. g. a terrestrial TV antenna (16) and a TV cable network (18). The circuit comprises first SPST switches (28, 30), each connected to one of the input terminals and a second, SPDT switch (32) connected to the first SPST switches. The switch circuit achieves high isolation performance between the input terminals (20, 22). (end of abstract)
Agent: Philips Intellectual Property & Standards - Briarcliff Manor, NY, US Inventor: Kong Lim Toh USPTO Applicaton #: 20060208826 - Class: 333103000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060208826. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to electrical circuits, more particularly to a Radio Frequency (RF) switch circuit and to a receiver circuit for receiving a radio frequency signal. [0002] A receiver circuit serves to receive a RF signal. The RF signal can contain either an analogue or a digital signal. The receiver circuit converts the received RF signal to an Intermediate Frequency (IF) signal, and then to a baseband signal. In the case where the received RF signal contains a digital signal, the output is a digital signal, e. g. an MPEG-2 transport stream. In the case where the RF signal contains an analogue signal, the output is an analogue baseband signal, e. g. an NTSC signal. [0003] A switch circuit serves to connect and disconnect electrical signal paths. For example, several signal sources can be connected to one signal input by a switch circuit. The switch circuit allows to select one of the signal sources and connect it to the signal input. [0004] Especially for RF applications a switch circuit needs to fulfill certain requirements. One of the requirements would be a low insertion loss (IL) in the forward path. Another would be the isolation performance between not-selected signal sources and the signal input as well as between signal sources. [0005] It is known that commercially available cable Set-Top-Boxes (STB) make use of two or more signal sources, such as for cable and terrestrial TV-signals. In these devices, switching between the two signal sources is achieved by means of electromechanical assemblies which require an electric current to magnetize a coil, which then makes or breaks contact between two contact pins, thereby performing the function of a mechanical switch. Such electromechanical assemblies are bulky and require relatively high current and high voltage to control. [0006] U.S. Pat. No. 5,274,343 discloses a radio frequency circuit for a radar system, connecting several RF signal sources to a single input port of a frequency multiplier circuit. The circuit works as an RF switch circuit with cascading first and second switches, interconnected by a propagation net work. First and second switches are SPDT (single pole double throw) integrated FET switches, each comprising one common port and two branch ports. In each of the first switches, one branch port is connected to a termination impedance and the other is connected via a propagation network to a branch port of one of the second switches. The common ports of the second switches are connected to an input port via a network. [0007] It is the object of the present invention to provide a switching circuit and a receiver circuit for electronically switching between at least two signal sources, which circuits are simple in structure and provide good isolation performance. [0008] This object is achieved by a switch circuit according to claim 1 and by a receiver circuit according to claim 9. Dependent claims refer to preferred embodiments. [0009] According to the invention, a switch circuit is provided with at least two input terminals and one output terminal. For RF signals applied to the two input terminals, signal paths are selectively provided to the output terminal. This is achieved by cascading first and second switches. [0010] The first switches comprise a first and a second port. The switches are electronically switchable such that in a first state the first and second ports are connected, whereas in a second state the first and second ports are disconnected. This leads to a high insertion loss in the disconnected state (e.g. more than 40 dB typically) and low insertion loss (e.g. less than 3 dB, typically about 1 dB) in the connected state. [0011] In a preferred embodiment the first switches are implemented using PIN diodes. It is preferred to use two anti-parallel PIN diodes in series connection between first and second ports, and a driver terminal connected between the PIN diodes. Also it is preferred for the first switches to be comprised of discrete electronic parts. [0012] According to the invention, there is provided as the second stage of the switch cascade a second switch including two branch ports and a common port. The second switch functions as a single-pole-multi-throw (SPMT) switch, selectively connecting one of the branch ports to the common port. It is preferred to use a switch with only two branch ports, hence a single-pole-double-throw (SPDT) switch. According to a preferred embodiment of the invention, an integrated circuit SPDT or SPMT switch is used for the second switch, e.g. an integrated circuit using FET switches. [0013] According to the invention, in the switch circuit each input terminal is connected to one of the branch ports of the second switch via one of the first switches. Thus, the signal paths are completely electronically switchable. Part count for this circuit is low. In terms of isolation performance, high values can be achieved because of the cascaded structure. E.g. if each switching stage provides minimum 35 dB isolation in a relevant frequency range such as from 50 to 500 MHz, the total isolation performance will be a minimum of 70 dB. [0014] According to a preferred embodiment of the invention, a control circuit is provided for the first switches. The control circuit preferably comprises at least two driver circuits, one to provide a control signal and to drive one of the first switches therewith, and the other to provide an inverted control signal and drive another of the first switches therewith. This allows to control both switches with only one control signal, provided at a control terminal. It is preferred for the control circuit to be comprised of discrete electronic parts. [0015] According to a further development of the invention, both first and second switches are controlled simultaneously. Preferably, the above described control circuit is also connected to the second switch, controlling it synchronously to the first switches. This allows for a compact switch circuit already including other circuitry for both switches. [0016] According to a preferred embodiment of the invention, an I2C transceiver is connected to the control circuit. The I2C bus is a simple means of communication and control, for which inexpensive highly integrated components are available. [0017] According to another aspect of the invention, a receiver circuit for receiving a radio frequency signal is provided comprising a switch circuit as described above connected to the input of a tuner circuit. The switch circuit serves to select one out of at least two RF signal sources to connect to the tuner input terminal. For example, the two signal sources could be a terrestrial TV antenna and a cable TV network. The tuner preferably comprises wide band circuitry, able to process the complete frequency range of both signal sources. Due to the excellent isolation performance of the switch circuit, the two signal sources are well isolated from each other. Thus, one tuner can be used for signals from two different sources, electronically switching between the two. [0018] In the following, a preferred embodiment of the invention will be described with reference to the figures. These are: [0019] FIG. 1 a schematic representation of a receiver set connected to a terrestrial TV antenna and a cable TV network; [0020] FIG. 2 a schematic circuit diagram of an RF switch circuit used in FIG. 1; [0021] FIG. 3 a schematic circuit diagram of a first switch used in FIG. 2; [0022] FIG. 4 a schematic circuit diagram of a second switch used in FIG. 2; [0023] FIG. 5 a schematic circuit diagram of a driver circuit used in FIG. 2. [0024] Shown in FIG. 1, there is a receiver set 11 comprising a TV device 14 and a Set-Top-Box 21. It should be noted that receiver set 11 serves here as an example only. TV device 14 can be any visual display, e. g. in the form of a LCD-, Plasma- or Cathode Ray display. Also, receiver set 11 can be a computer system where there is a TV card installed instead of Set-Top-Box 21 and there is a computer monitor instead of TV device 14. Also as a further alternative, the functions of Set-Top-Box 21 can be integrated in a TV device. Continue reading... Full patent description for Electronically controllable rf switch Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electronically controllable rf switch patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Electronically controllable rf switch or other areas of interest. ### Previous Patent Application: Transmission line transition Next Patent Application: 90-degree hybrid Industry Class: Wave transmission lines and networks ### FreshPatents.com Support Thank you for viewing the Electronically controllable rf switch patent info. IP-related news and info Results in 0.55961 seconds Other interesting Feshpatents.com categories: Software: Finance , AI , Databases , Development , Document , Navigation , Error |
||
